As part of the on-going evolution of the third Generation Partnership Project (3GPP) Wideband Code Division Multiple Access (WCDMA) standard, Dual-Cell High-Speed Downlink Packet Access (HSDPA) (DC-HSDPA) has been approved in 3GPP. Dual-cell HSDPA is a natural evolution of High Speed Packet Access (HSPA) which allows the use of a second HSPA carrier (i.e. two 5 MHz downlink carriers) to create a bigger downlink data pipe.
The DC-HSDPA operation is backward compatible with Release 7, 6, and 5, and Release 99 devices through seamless interoperation between single-carrier and dual-carrier coverage areas. Dual-cell operation provides both throughput increase and latency reduction. Most importantly, more wireless transmit receive units (WTRUs) have access to higher data rates, especially in poor radio conditions where techniques such as Multiple Input Multiple Output (MIMO) are not used. In terms of system performance, Dual-Cell HSDPA offers efficient load balancing across carriers and some capacity gain.
The agreed dual-cell operation in Release 8 of the 3GPP standard only applies to the downlink, with the uplink (UL) transmission restricted to a single cell, i.e. carrier. Furthermore, the following additional restrictions have been imposed: the two downlink cells belong to the same Node-B and are on adjacent carriers (and by extension the carriers are in the same frequency band); and the two downlink cells cover the same geographical area (sector). Accordingly, a dual-cell capable WTRU communicates configured to receive two downlink carriers (an anchor carrier and a supplementary carrier), and to transmit one uplink anchor carrier. The downlink anchor carrier is matched with the uplink anchor carrier.
With respect to mobility, the WTRU bases all its mobility decisions on the anchor cell. Since the supplementary carrier is restricted in Release 8 to be adjacent to the anchor carrier, the pathloss between the two cells and the WTRU is similar. Therefore, it was decided that there was no need for the perform mobility procedures based on the supplementary carrier.
As the scope of dual-cell operation is expanded in future WCDMA releases or in other wireless systems, for example, to non-adjacent frequencies or across frequency bands, mobility procedures (e.g., measurement reporting) and others procedures will be impacted. Therefore, there exists a need for an improved method and apparatus for dual cell operation.